As the continuous development of industries, automatic welding machines, welding robots and their control methods have been developed rapidly in order to meet the demands of continuous increase of workload and requirement of welding quality. But up to the moment there is no arc welding robot which can be used for welding of large structures on site. Speaking generally there are mainly two methods for realizing automation of welding at the moment:
1) Arm Type Industrial Arc Welding Robot
This type of robot normally has six and half axis of freedom, which cooperates with the manipulator having three or more axis of freedom. The robot automatically tracks the seam and performs the welding by means of off-line programming or teaching.
This type of robot has limitations in its dimension, it can be used only in workshop for welding of small work-piece or small size structure such as small boat or carriage.
2) Track Crawling Type Partially Intelligent Automatic Arc Welding Machine
This type of automatic welding machine is capable of carrying out the welding of large structures by mainly placing a carriage on track, wherein the carriage has welding torch and performs the welding along the track. There exist problems in this type of automatic welding machine: it is difficult for the profile of the track to be completely the same as those of the work-piece to be welded, although the tracks are divided into rigid and flexible types; despite that the tracks are substantially installed along the welding seam, the tracks are not often completely in parallel with the welding seam, especially when the work-piece has a curved seam and different types of joint; although in some cases it is equipped with automatic tracking mechanism, the tracking capabilities are limited, because the tracks are limited and thereby the range of tracking is very small. In addition, the installation of the tracks is time-consuming and costly, wherein the installation of the tracks often takes half of the workload and the cost of the tracks accounts for more than one third of the total investment in the equipment.